Process for making 1,3-dioxane derivatives

ABSTRACT

The invention provides a novel process for making novel (4-phenyl-1,3-dioxan-cis-5-yl)alkenoic acids of the formula I in which Ra and Rb are independently hydrogen, alkenyl, alkyl, halogenoalkyl, pentafluorophenyl, aryl or aryl-(1,4C)alkyl; or Ra and Rb together are polymethylene; Rc is hydroxy or (1-6C)alkanesulphonamideo, A is vinylene, n is 1, Y is polymethylene, and benzene ring B bears various optional substituents. The process involves the reaction of an aldehyde of formula II with an ylid to give an erythro-diol of formula III which is then cyclized to the required dioxane derivative of formula I. The invention also provides a novel process for making the aldehydes of formula II from the corresponding lactols of formula IIa, which are themselves obtained with the correct trans-stereochemistry by two selective reductions of a trans-phenylparaconic acid of formula V. The compounds of formula I are useful as thereapeutic agents.

This is a division of application Ser. No. 670,016 filed Nov. 9, 1984,now U.S. Pat. No. 4,723,037.

This invention concerns a novel chemical process for the production ofnovel (4-phenyl-1,3-dioxan-cis-5-yl)alkenoic acid derivatives whichantagonise one or more of the actions of thromboxane A₂ (TXA₂) and areof value as therapeutic agents. The invention is also concerned withvarious 2-phenyl-tetrahydrofuran derivatives which are valuable chemicalintermediates, for example for use in the above mentioned process.

In European patent application, publication No. 94239A2, (hereafter EPANo. 94239), there is described a series of(4-phenyl-1,3-dioxan-cis-5-yl)alkenoic acids of the formula I (set outhereinafter) wherein Ra and Rb are independently hydrogen,(2-6C)alkenyl, (1-8C)alkyl optionally bearing up to three halogenosubstituents, pentafluorophenyl, aryl or aryl-(1-4C)alkyl, the lattertwo of which may optionally bear up to three substituents selected fromhalogeno, (1-6C)alkyl, (1-6C)alkoxy, (1-4C)alkylenedioxy,trifluoromethyl, cyano, nitro, hydroxy, (2-6C)alkanoyloxy,(1-6C)alkylthio, (1-6C)alkanesulphonyl, (1-6C)alkanoylamino, andoxapolymethylene of 2 to 4 carbon atoms, provided that when both Ra andRb are alkyl or alkenyl, the total number of carbon atoms in Ra and Rbtaken together is 8 or less; or Ra and Rb together form polymethylene of2 to 7 carbon atoms, optionally bearing one or two (1-4C)alkylsubstituents; Rc is hydroxy, (1- 6C)alkoxy or (1-6C)alkanesulphonamido;n is the integer 1 or 2; A is ethylene or vinylene; Y is polymethyleneof 2 to 5 carbon atoms optionally bearing (1-4C)alkyl as a substituent;benzene ring B optionally bears one or two substituents selected fromhalogeno, (1-6C)alkyl, (1-6C)alkoxy, hydroxy, (1-6C)alkanoyloxy,(1-6C)alkanoylamino, trifluoromethyl and nitro; and the substituents atpositions 4 and 5 of the dioxane ring have cis-relative stereochemistry;or for those compounds wherein Rc is hydroxy, a salt thereof with a baseaffording a physiologically acceptable cation. The compounds aredisclosed as antagonising one or more of the actions of thromboxane A₂and are of value as therapeutic agents.

The compounds of formula I contain at least two asymmetric carbon atoms(i.e. at C₄ and C₅ of the dioxane ring) and may exist and be isolated inracemic and optically active forms. In addition those compounds offormula I wherein A is vinylene exist, and may be isolated, in separatestereoisomeric forms (`E` and `Z`) about that group. The terms Ra, Rband Rc etc, are used to depict generic radicals and have no othersignificance.

Specific combinations of Ra and Rb which are disclosed as preferred are,by way of example:

(i) Ra and Rb are both hydrogen, methyl, ethyl, propyl, butyl ortrifluoromethyl;

(ii) one of Ra is hydrogen and the other is trifluoromethyl,chloromethyl, benzyl, isopropyl, hexyl, octyl, phenyl (optionallybearing 1 or 2 fluoro, chloro, bromo, methyl, methoxy, trifluoromethyl,hydroxy, cyano, methylthio or acetamido), phenyl bearing methylenedioxyor methyleneoxymethylene (--CH₂ OCH₂ --), pentafluorophenyl, 1-naphthylor 2-naphthyl; and

(iii) Ra and Rb together form trimethylene, tetramethylene,pentamethylene, hexamethylene or a group of the formula: --CH₂CH₂.CHCH₃.CH₂ CH₂ --.

Specific preferred values for Ra or Rb when it is a mono ordisubstituted phenyl are, for example, 2-fluoro-, 3-fluoro-, 4-fluoro-,2-chloro-, 3-chloro-, 4-chloro-, 2-bromo-, 3-bromo-, 4-bromo-,2-methyl-, 3-methyl-, 4-methyl-, 2-methoxy-, 3-methoxy-, 4-methoxy-,2-trifluoromethyl-, 3-trifluoromethyl-, 4-trifluoromethyl-, 3-hydroxy-,4-cyano-, 4-methylthio-, 4-acetamido-, 3,4-dichloro-, 2,4-dimethyl-,3,4-methylenedioxy- and 3,4-(methyleneoxymethylene)-phenyl.

Specific preferred values for benzene ring B are, for example, when itis phenyl, or 2-fluoro-, 2-chloro-, 2-bromo-, 2-methyl-, 2-ethyl-,2-isopropyl-, 2-methoxy-, 2-hydroxy-, 3-fluoro- or 3-chloro-phenyl.

A further preferred group of acids disclosed in EPA No. 94239 comprisescompounds of the formula Ib wherein:

Ra and Rb are both hydrogen, methyl, ethyl, propyl, butyl, ortrifluoromethyl;

(ii) or together form trimethylene, tetramethylene, pentamethylene,hexamethylene or a group of the formula: --CH₂ CH₂.CHCH₃.CH₂ CH₂ --; or

(iii) Ra is (3-8C)alkyl, trifluoromethyl, chloromethyl, 2-chloroethyl,pentafluorophenyl, or phenyl, benzyl or naphthyl, the last three ofwhich may optionally bear 1 or 2 halogeno, (1-4C)alkyl, (1-4C)alkoxy,trifluoromethyl, hydroxy, cyano, (1-4C)alkylthio or (1-4C)alkanoylaminosubstituents, or a methylenedioxy or methyleneoxymethylene substituent,and Rb is hydrogen;

benzene ring B is unsubstituted or is 2-halogeno-, 2-(1-4C)alkyl-,2-(1-4C)alkoxy-, 2-hydroxy- or 3-halogeno-phenyl;

Ra and the substituents at the 4- and 5-positions of the dioxane ringhave cis-relative stereochemistry; and the carbon atoms adjacent to thevinylene group have the indicated cis-relative stereochemistry; or asalt thereof with a base affording a physiologically acceptable cation;or a methyl or ethyl ester thereof; or a methanesulphonamido,ethanesulphonamido or 1-methylethanesulphonamido

Particular salts of compounds of formula Ib or I (wherein Rc is hydroxy)which are disclosed include, for example, alkali metal and alkalineearth metal salts such as lithium, sodium, potassium, magnesium andcalcium salts, aluminium and ammonium salts, and salts with organicamines or quaternary bases forming physiologically acceptable cations.

A preferred compound disclosed in EPA No. 94239 is5(Z)-7-(2,2-dimethyl-4-o-methoxyphenyl-1,3-dioxan-cis-5-yl)heptenoicacid.

A major problem in the production of compounds of the formula I lies inarranging for the correct cis-relative stereochemistry at positions 4,5of the dioxane ring. In EPA No. 94239, this problem is solved bychromatographic separation of cis-/trans- stereoisomeric mixtures at oneor more stages in the synthetic sequence. The process of the presentinvention avoids such a separation of stereoisomers by incorporating thecorrect relative stereochemistry at an early point in the syntheticprocedure. The process of the invention also avoids the use of ozonewhich is used in the synthetic sequence disclosed in EPA No. 94239 andis readily adapted to produce optically active forms of the formula Icompounds.

According to the invention there is provided a process for themanufacture of a compound of formula I as defined hereinbefore butwherein n is 1, A is vinylene and Rc is hydroxy or(1-6C)alkanesulphonamido which comprises the steps of:

(i) reacting an erythro-4-hydroxy-3-hydroxymethyl-4-phenylbutyraldehydeof the formula II, or an alkali metal salt thereof, with an ylid of theformula:

    (Rd).sub.3 P=CH.Y.CO.Q

wherein Rd is (1-6C)alkyl (especially methyl or ethyl) or aryl(especially phenyl) and when Rc is hydroxy, Q stands for --OM in which Mis an alkali metal such as lithium, sodium or potassium and, when Rc is(1-6C)alkanesulphonamido, Q stands for --NM.SO₂ Re in which Re is (1-6C)alkyl such as methyl or ethyl and M has the meanings stated above, togive after acidification an erythro- diol of the formula III wherein Rfhas the limited meanings for Rc defined above; and

(ii) reacting the diol of formula III, or a mono (1-6C)alkanesulphonylor arenesulphonyl ester thereof, with a carbonyl compound of the formulaRaRb.CO, or an acetal hemiacetal or hydrate thereof.

It will be appreciated that the above process can be readily adapted tothe production of compounds of the formula I wherein A is ethylene byinterposing a conventional catalytic hydrogenation step after the aboveWittig reaction (i) or cyclisation reaction (ii). Such a hydrogenationmay be carried out in a suitable solvent or diluent, for example a(1-4C)alkanol (such as ethanol or 2-propanol), optionally in thepresence of water, and at a temperature in the range, for example, 15°to 35° C., using hydrogen at a pressure of, for example, 1 to 2atmospheres. A suitable catalyst is, for example, a noble metal catalystsuch as palladium metal conveniently on an inert support such as carbon,barium sulphate or barium carbonate.

Similarly, when a compound of formula I wherein Rc is (1-6C)alkoxy isrequired, the corresponding acid of formula I wherein Rc is hydroxy, ora reactive derivative thereof, is esterified using a conventionalprocedure, starting from the free acid or a reactive derivative.

When a free acid of formula I is used, it is particularly convenient toperform the process in the presence of a suitable dehydrating agent, forexample dicyclohexylcarbodiimide, in the presence of a suitable solventor diluent for example tetrahydrofuran, acetone, methylene chloride or1,2-dimethoxyethane, at a temperature in the range, for example, 10° to50° C., but preferably at or near room temperature.

A suitable reactive derivative of an acid of formula I is, for example,an acid chloride, bromide, anhydride, mixed anhydride with formic acid,or an azide, which may be produced from the free acid in conventionalmanner. When such a derivative is used, no additional dehydrating agentis necessary, and the (1-6C)alkanol is conveniently present in largeexcess, optionally diluted with a suitable diluent or solvent such as anether, for example tetrahydrofuran or 1,2-dimethoxyethane.

Compounds of formula I wherein Rc is (1-6C)alkanesulphonamido may beobtained by carrying out the above process to produce an acid of formulaI wherein Rc is hydroxy followed by a conventional sulphonamidationanalogous to the above described esterification. Thus, for example afree acid of formula I wherein Rc is hydroxy may be reacted with a(1-6C)alkanesulphonamide together with a suitable dehydrating agent, forexample dicyclohexylcarbodiimide, optionally together with an organicbase, for example 4-dimethylaminopyridine, in the presence of a suitablesolvent or diluent, for example methylene chloride at a temperature inthe range, 10° to 50° C., but preferably at or near room temperature.Alternatively, a reactive derivative of an acid of formula I, wherein Rcis hydroxy, for example an acid halide (such as the acid chloride) maybe reacted with an alkali metal salt (such as the sodium salt) of theappropriate (1-6C)alkanesulphonamide, conveniently at or near roomtemperature and in a suitable solvent or diluent, for example an ether,N,N-dimethylformamide or methylene chloride.

When a salt of a compound of formula I wherein Rc is hydroxy isrequired, it may be obtained, for example, by reaction with theappropriate base affording a physiologically acceptable cation.

Further, when an optically active form of a compound of formula I isrequired, the process of the invention is carried out using an opticallyactive starting material of formula II or III. Alternatively, when Rc ishydroxy, a racemic form of the said compound may be reacted with anoptically active form of a suitable organic base, for example ephedrine,N,N,N-trimethyl (1-phenylethyl)ammonium hydroxide or 1-phenylethylamine,followed by conventional separation of the diastereoisomeric mixture ofsalts thus obtained, for example by fractional crystallisation from asuitable solvent, for example a (1-4C)alkanol, whereafter the opticallyactive form of said compound of formula I may be liberated by treatmentwith acid using a conventional procedure for example using an aqueousmineral acid such as dilute hydrochloric acid. Similarly, when anoptically active form of a compound of formula I wherein Rc is otherthan hydroxy is required, it may be obtained using the aforementionedesterification or sulphonamidation procedures using the appropriateoptically active form of said acid.

Further it will be appreciated that when a compound of formula I whereinRa or Rb is hydroxyphenyl, or benzene ring B bears a hydroxy substituentis required, this may conveniently be obtained by carrying out reaction(i) and (ii) hereinabove using a corresponding furan of formula II anddiol of formula III in which the aromatic hydroxy substituent isprotected, for example as a trimethylsilyl, (1-6C)alkyl (such as methylor ethyl) or acyl (such as acetyl or benzoyl) derivative, followed by anextra and final deprotection step. A process incorporating such adeprotection step after reactions (i) and (ii) is also provided as afeature of the invention.

The deprotection conditions required necessarily depend on theprotecting groups concerned. Thus, for example, when it is methyl orethyl the deprotection may be carried out, for example, by heating withsodium thioethoxide in a suitable solvent (such asN,N-dimethylformamide) at an elevated temperature, for example 90°-160°C. Similarly, when the protecting group is acyl, it may be removed, forexample by hydrolysis in the presence of a base (such as sodium orpotassium hydroxide) in a suitable aqueous solvent [such as a(1-4C)alkanol or a glycol] at a temperature in the range, for example,10°-60° C. Similarly in the case of a trimethylsilyl protecting group,it may be removed for example, by reaction with aqueoustetrabutylammonium fluoride or sodium fluoride in conventional manner.

The Wittig reaction involved in step (i) in general produces compoundsof formula I in which the carbon atoms adjacent to the vinylene grouphave predominantly cis-relative stereochemistry i.e. the "Z" isomer.However, the compounds of formula I having trans-relativestereochemistry (i.e. the "E" isomer) are also formed in the process andmay be obtained by conventional separation of the mixture of "Z"- and"E"-isomers first obtained.

The reaction step (i) is conveniently performed in a suitable solvent ordiluent, for example an aromatic solvent such as benzene, toluene orchlorobenzene, an ether such as 1,2-dimethoxyethane, dibutyl ether,tetrahydrofuran, dimethyl sulphoxide or tetramethylene sulphone, or in amixture of one or more such solvents or diluents. Reaction step (i) isgenerally performed at a temperature in the range, for example, -80° C.to 40° C. but is conveniently performed at or near room temperature,that is in the range 15° to 35° C. Reaction step (i) may be operatedquite independently of step (ii), since the erythro-diols of formula IIIare useful chemical intermediates for the production of other compoundsbesides those of formula I.

The ylid starting materials may be obtained by procedures analogous tothose well known in the art. Thus, they may be obtained by treating aphosphonium halide of the formula:

    (Rd.sub.3) P.sup.+.CH.sub.2.Y.CO Qa Z.sup.-

wherein Rd and Y have the meanings stated above and Qa is hydroxy or(1-6C)alkanesulphonamido and Z is halide, with a strong base such assodium hydride, lithium diisopropylamide, potassium t-butoxide orbutyllithium in a suitable solvent such as that used for the Wittigreaction itself. The ylid starting materials are generally formed insitu immediately prior to carrying out the process of the invention.

Aldehydes of formula II having the required erythro-diol configurationmay be conveniently formed in solution as the corresponding alkali metalsalts by reaction of a[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-phenylfuran of theformula IIa (that is the corresponding lactol formed from the aldehydeof formula II) with an alkali metal derived base, such as potassiumt-butoxide or butyllithium, in a suitable inert solvent, and this is thebasis for the invention. The aldehydes of formula II are preferablygenerated and reacted as required in situ. The invention thus alsoprovides a process for the production of a diol of the formula III whichcomprises carrying out step (i) of the above process but using a lactolof formula IIa as original starting material to generate the aldehyde IIin situ.

In the cyclisation reaction (ii), a suitable (1-6C)alkanesulphonyl esteris, for example, a methanesulphonyl or ethanesulphonyl mono-ester and asuitable arenesulphonyl ester is, for example, a benzenesulphonyl orp-toluenesulphonyl mono-ester.

The carbonyl compound of the formula RaRb.CO (or its hydrate, or itsacetal or hemiacetal with a (1-4C)alkanol) is preferably used in excess.

When the free diol of formula III is used the reaction (ii) is carriedout in the presence of an acid catalyst, for example, hydrogen chloride,hydrogen bromide, sulphuric acid, phosphoric acid, p-toluenesulphonicacid or the anionic form of a sulphonated polystyrene catalyst,conveniently in a suitable solvent or diluent, for example an ether suchas diethyl ether, dibutyl ether, 1,2-dimethoxyethane or tetrahydrofuran,and at a temperature in the range, for example, 10° to 120° C. In somecases sufficient acid catalyst may be provided by the inherent acidityof the starting diol of formula III wherein Rc is hydroxy.

When a monosulphonyl ester of a diol of formula III is used, thecyclisation reaction (ii) is carried out first in the presence of anacid catalyst, for example under the conditions described above toproduce an intermediate of the formula IIIa, wherein one of Xa and Xb isalkanesulphonyl or arenesulphonyl, and the other is a group of theformula --CRaRb.OH. The latter intermediate may then be cyclised in situto the required compound of formula I by addition of a suitable base,for example, sodium hydride,butyllithium or potassium carbonate, in asuitable solvent or diluent, for example in the ether solvent used forthe acid catalysed step above, and at a temperature in the range, forexample, 30°-100° C.

The mono-sulphonyl esters may be made by any conventional procedures,for example by reacting one molecular equivalent of the appropriatealkanesulphonyl or arenesulphonyl halide, for example methanesulphonylchloride or p-toluenesulphonyl chloride, in a suitable solvent ordiluent (such as an ether or dichloromethane) and in the presence of abase such as pyridine or triethylamine.

The majority of erythro-diols of formula III are disclosed in general inEPA No.94239. The aldehydes of formula II and the corresponding[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-phenylfurans offormula IIa, wherein Q, Y and benzene ring B have the meanings set outhereinbefore, are novel and are provided as further features of theinvention.

The invention also provides a process for the manufacture of a[2,3-trans]-tetrahydrofuran derivative of formula II which comprisesselectively reducing a [2,3-trans]-lactone of the formula IV whereinbenzene ring B has the meaning set out hereinbefore.

The selective reduction may be carried out using any suitable reducingagent known to selectively reduce the lactone carbonyl group to thecorresponding lactol. Thus, typical reducing agents are, for example,diisobutylaluminium hydride or sodium(t-butoxy)bis(2-methoxyethoxy)aluminium hydride. The reduction ispreferably performed in a suitable solvent or diluent, for example anether such as diethyl ether, 1,2-dimethoxyethane or tetrahydrofuran,conveniently diluted with a hydrocarbon solvent such as benzene, tolueneor xylene, and at a temperature in the range, for example, -80° to +20°C.

The lactones of formula IV may themselves be obtained by selectivereduction of a trans-phenylparaconic acid of the formula V (or aderivative thereof), which reductive process is provided as a furtherfeature of the invention.

This selective reduction may be carried out by means of any suitablereducing agent known to selectively reduce carboxylic acid groups in thepresence of lactone carbonyl groups. Thus, for example typical reducingagents are diborane or alkali metal borohydrides (such as sodiumborohydride) in the presence of a Lewis acid such as tin(IV) chloride.Examples of suitable derivatives are, for example acid halides such asacid chlorides or bromides. The reduction is preferably carried out in asuitable solvent or diluent, for example as mentioned hereinabove forthe preparation the compounds of formula II, and at a temperature in therange, for example, 0° to 35° C.

The lactones of formula IV and certain of the paraconic acids of formulaV wherein benzene ring B has the meanings set out herein are novel andare provided as still further features of the invention.

The paraconic acids of formula V may be made by the base-catalysedreaction of a suitable benzaldehyde of the formula VI with succinicanhydride and this process addressed to novel acids of formula V isprovided as a further feature of the invention.

A suitable base catalyst is, for example sodium acetate or zinc chloridetriethylamine complex. However other base catalysts previously used forthe production of known paraconic acids (such as phenylparaconic acid)may also be employed. A suitable solvent or diluent, for examplemethylene chloride may be used. The reaction may also be performed inthe absence of solvent. A convenient temperature is, for example in therange, 10° C. to 130° C.

The procedure may give rise to both cis-paraconic acids of formula Va aswell as the required trans-paraconic depending on the reactionconditions. However the acids of formula Va may be readily converted tothe thermodynamically more stable trans-isomer of formula V by treatmentwith strong acid. The latter process is also provided as a feature ofthe invention. A suitable strong acid is, for example a mineral acidsuch as sulphuric or phosphoric acid, or an organic acid such asp-toluenesulphonic or trifluoroacetic acid.

It will be appreciated that when a compound of formula I which is inoptically active form is required, it is possible to produce such acompound by starting with a single, optically active, enantiomeric formof a trans-paraconic acid of formula V and carrying out theaforementioned processes via the intermediates of formula IV, IIa, IIand III. Such a combined process, whether for the production of aracemic or a single optically active form of a compound of formula I asdefined hereinbefore but wherein n is 1, A is vinylene and Rc is hydroxyor (1-6C)alkanesulphonamido, is provided as a further feature of theinvention.

The invention, accordingly, also provides the novel intermediates offormula V, IV, and IIa and II as defined hereinbefore in separateoptically active forms as well as in racemic form.

It will be understood that one or more of the above procedures may becarried out in succession in the same reaction vessel and without theisolation or purification of the appropriate intermediate.

The invention will now be illustrated by the following non-limitingExamples in which, unless otherwise stated:

(i) evaporations were carried out on a rotary evaporator in vacuo;

(ii) operations were carried out at room temperature, that is in therange 18° to 26° C.;

(iii) the progress of chemical reactions was assessed by thin layerchromatography (TLC) on 0.25 mm. Kieselgel 60F 254 plates (Art. 5715),available from E Merck, Darmstadt, W. Germany.

(iv) NMR spectra were determined at 90 MHz in CDCl₃ usingtetramethylsilane (TMS) as an internal standard and expressed aschemical shifts (delta values) in parts per million relative to TMS formajor peaks, using the following abbreviations for designation of peaks:s, singlet; d, doublet; t, triplet; m, multiplet; br, broad;

(v) yields are provided for illustration and do not represent themaximum attainable by diligent development of the disclosed procedures;and

(vi) end-products were characterised by standard techniques ofmicro-analysis, infra-red, NMR and/or mass spectral analysis.

EXAMPLE 1

This Example illustrates the production of a paraconic acid of formulaV.

Succinic anhydride (22 g.), o-methoxybenzaldehyde (20 g.) and anhydrouszinc chloride (44 g.) were added to dichloromethane (dried over alumina,200 ml.) and the mixture stirred under argon. Triethylamine (41 ml.) wasadded to the ice-cooled mixture over a period of 20 minutes. Thereaction mixture was then stirred at 20°-25° C. for 18 hours, afterwhich time hydrochloric acid (2M,130 ml.) and ethyl acetate (200 ml.)were added. The subsequent mixture was stirred for 5 minutes. Theaqueous phase was separated and extracted with ethyl acetate (150 ml.)The combined extracts were washed with saturated brine (50 ml.) and thenextracted with saturated sodium bicarbonate solution (3×200 ml.). Thecombined aqueous extracts were washed with ethyl acetate, and thenacidified to pH2 with concentrated hydrochloric acid. The oil whichseparated was extracted into ethyl acetate (2×150 ml.). The combinedextracts were washed with saturated brine (4×50 ml.) until acid free,then dried (MgSO₄) and evaporated. Toluene (300 ml.) was added to theresidue and the mixture was distilled atmospheric pressure until theresidual material attained 110° C. On cooling to 20° C.,tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid separated as acrystalline white solid (27.2 g., 78%) (m.p. 106° C.) which was shown byNMR to be a mixture of [2,3-cis-]- and [2,3-trans]-isomer: 2.8-3.0(2H,m), 3.1-3.6 (1H,m), 3.8 (3H,s), 5.82 (3/4H,d) [trans], 5.95 (1/4H,d) [cis], 6.8-7.5 (4H,m).

EXAMPLE 2

This Example illustrates the isomerisation of a cis- to atrans-paraconic acid of formula V.

A mixture of [2,3-cis]- and[2,3-trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid(188.6 g.) was added to an ice cooled solution of concentrated sulphuricacid (320 ml.) in water (480 ml.) and stirred at 20°-25° C. for 18hours. Water (800 ml.) was then added and the mixture extracted withethyl acetate (2×750 ml.). The combined extracts were washed with brine(4×500 ml.) until acid free, dried (MgSO₄) and evaporated to low volume.Toluene (1 liter) was added and the distillation continued atatmospheric pressure until the residual material attained a temperatureof 110° C. On cooling pure[2,3-trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acidseparated as a white crystalline solid (169.5 g.,90%), m.p. 133°-134°C.; NMR: 2.8-3.0 2H,d), 3.3-3.6 (1H,m), 3.8 (3H,s), 5.82 (1H,d), 6.8-7.4(4H,m).

EXAMPLE 3

This Example illustrates the selective reduction of a paraconic acid offormula V to give a lactone of formula IV.

Borane solution in tetrahydrofuran(THF) (1M, 254 ml.) was added during15 minutes to a stirred solution of[2,3-trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid(20 g.) in THF (50 ml.) at 20° to 25° C. After a further 45 minuteswater (10 ml.) was added slowly to destroy excess borane, followed bysaturated potassium carbonate solution (50 ml.). The mixture was wellagitated and allowed to separate. The aqueous phase was extracted withethyl acetate (250 ml.). The organic phases were combined, washed withsaturated brine (50 ml.), dried (MgSO₄) and evaporated to dryness toyield[4,5-trans]-tetrahydro-4-hydroxymethyl-5-o-methoxyphenylfuran-2-one(18.0 g.) as a viscous, colourless oil, essentially pure by TLC and NMRspectroscopic analysis.

EXAMPLE 4

This Example illustrates the selective reduction of a lactone of formulaIV to a lactol of formula IIa.

Diisobutylaluminium hydride solution in toluene (1.23M, 35.3 ml.) wasadded during 15 minutes to a stirred solution of[4,5-trans]-tetrahydro-4-hydroxymethyl-5-o-methoxyphenylfuran-2-one (4.5g.) in toluene (20 ml.) and 1,2-dimethoxyethane (4 ml.) cooled at -60°to -70° C.* under argon. After 20 minutes, methanol (6 ml.) was addedand the reaction mixture was allowed to attain room temperature.Saturated brine (50 ml.) and ethyl acetate (100 ml.) were then added andthe mixture was stirred vigorously for 15 minutes. Insoluble materialwas removed by filtration through diatomaceous earth. The phases wereseparated and the aqueous phase extracted with ethyl acetate (50 ml ).The combined organic phases were dried (MgSO₄), evaporated and theresidue recrystallised from toluene to give[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-o-methoxyphenylfuran(4.18 g.) as a white, crystalline solid, m.p. 110°-111° C. (mixture ofC5 epimers) of satisfactory purity, as judged by NMR espectroscopy, forfurther use.

EXAMPLE 5

This Example illustrates the formation of an erythro-diol of formulaIII.

A mixture of (4-carboxybutyl)triphenylphosphonium bromide (61.4 g.) andpotassium t-butoxide (31.0 g.) in dry toluene (500 ml.) was heated to90° C. for 30 minutes to form the cherry red ylid solution. A portion(210 ml) of this solution was then added to a solution of[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-o-methoxyphenylfuran(4.18 g.) in dry tetrahydrofuran 50 ml.) under argon. The reactionproduces the dipotassium salt oferythro-4-hydroxy-3-hydroxymethyl-4-o-methoxyphenylbutyraldehyde in situwhich reacts with the ylid. TLC analysis indicated the reaction wascomplete after 10 minutes. Water (220 ml.) was then added with vigorousstirring. The phases were separated and the aqueous phase extracted withether (4×100 ml.).

The extracts and solid interphase were discarded. The aqueous phase wasacidified to pH 4 with saturated oxalic acid solution and extracted withethyl acetate (3×200 ml.). These combined extracts were evaporated todryness. The white solid obtained was washed with ethyl acetate and thesolid discarded. The washings were then extracted with saturated sodiumbicarbonate solution (3×250 ml.). The aqueous extracts were againacidified to pH5 with saturated oxalic acid solution and theprecipitated material extracted with ethyl acetate (2×250 ml.). [In allextractions solid interphase material was removed by filtration]. Theethyl acetate extracts were evaporated and the residue dried byazeotropic distillation with toluene. There was thus obtainederythro-5-(Z)-9-hydroxy-8-hydroxymethyl-9-o-methoxyphenyl-5-nonenoicacid as a colourless oil (2.8 g.); NMR (400 MHz):1.50 (6H,m), 2.22(9H,m), 3.9 (3H,s), 4.0 (2H,m), 5.3 (3H,m), 7.1 (4H,m), 9.5 (1H,br s).

EXAMPLE 6

Using analogous procedures to those described in Examples 3-5, butstarting from the known compound[2,3-trans]-tetrahydro-5-oxo-2-phenyl-3-furancarboxylic acid, there maybe obtained 5(Z)-erythro-9-hydroxy-8-hydroxymethyl-9-phenylnonenoic acidas a viscous oil; NMR (400 MHz): 1.4-2.2 (7H,m), 2.86 (2H,t, J=7Hz),3.68 (2H,d), 4.8 (3H, br s), 4.99 (1H,d J=3.6 Hz), 5.2-5.6 (2H,m), 7.33(5H,s).

The following intermediates may be isolated:

(i) [4,5-trans]-tetrahydro-4-hydroxymethyl-5-phenylfuran-2-one; and

(ii) [2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-phenylfuran(mixture of C5 epimers).

EXAMPLE 7

This Example illustrates the cyclisation of an erythro-diol of formulaIII to give a dioxane of formula I.

A solution of erythro-5(Z)-9-hydroxy-8-hydroxymethyl-9-o-methoxyphenyl5-nonenoic acid (2.8 g.) in 2,2-dimethoxypropane (10 ml.) was treatedwith p-toluenesulphonic acid (0.05 g.). After 1 hour ether (10 ml.) andtriethylamine (0.1 ml.) were added. The solvents were evaporated and theresidue was dissolved in ether (20 ml.). The solution was washed withwater (3×10 ml.), then with saturated brine (10 ml.), dried (MgSO₄) andevaporated. The oily residue was extracted with boiling petrol (60°-80°C.) and the solution allowed to cool. There was thus obtained5(Z)-7-(2,2-dimethyl-4-o-methoxyphenyl-1,3-dioxan-cis-5-yl)heptenoicacid as a white crystalline solid (0.7 g.), m.p. 112°-114° C., having asatisfactory NMR spectrum: 1.55 (6H,d), 2.25 (2H,t), 1.1-2.7 (7H,m),3.6-4.3 (2H,m), 3.85 (3H,s), 5.1-5.6 (3H,m), 6.8-8.0 (4H,m), 10.3(1H,br).

Using a similar procedure to that described in Example 7 but startingfrom 5(Z)-erythro-9-hydroxy-8-hydroxymethyl-9-phenylnonenoic acid,5(Z)-7-(2,2-dimethyl-4-phenyl-1,3-dioxan-cis-5-yl)-heptenoic acid may beobtained as a solid, m.p. 86°-86.5° C. (after 3 recrystallisations fromhexane).

EXAMPLE 9

Using similar procedures to those described in Examples 3, 4, 5 and 7,the following compounds of formula Ib may be obtained by the processesof the invention via the corresponding intermediate diols of formulaIII, aldehydes of formula II, lactols of formula IIa, lactones offormula IV and carboxylic acids of formula V:

    ______________________________________                                        No.   Ra               Rb       Benzene Ring B                                ______________________________________                                        1     methyl           methyl   3-fluorophenyl                                2     methyl           methyl   3-chlorophenyl                                3     methyl           methyl   2-methylphenyl                                4     methyl           H        phenyl                                        5     isopropyl        H        phenyl                                        6     ethyl            ethyl    phenyl                                        7     ethyl            ethyl    2-fluorophenyl                                8     2-chlorophenyl   H        phenyl                                        9     2-methylphenyl   H        phenyl                                        10    2-ethylphenyl    H        phenyl                                        11    3-fluorophenyl   H        phenyl                                        12    3-chlorophenyl   H        phenyl                                        13    3-methylthiophenyl                                                                             H        phenyl                                        14    4-fluorophenyl   H        phenyl                                        15    4-chlorophenyl   H        phenyl                                        16    4-methoxyphenyl  H        phenyl                                        17    3,4-methylene    H        phenyl                                              dioxyphenyl                                                             18    3,4-(methylene-  H        phenyl                                              oxymethylene)-                                                          19    pentamethylene*           phenyl                                        20    hexamethylene*            phenyl                                        21    (3-methyl)pentamethylene*                                               ______________________________________                                         *Note: Ra + Rb taken together.                                           

EXAMPLE 10

The following additional sulphonamidation procedure illustrates theproduction of compounds of formula I wherein Rc is(1-6C)alkanesulphonamido:

A solution containing5(Z)-7-(2,2-dimethyl-4-phenyl-1,3-dioxan-cis-5-yl)heptenoic acid (318mg.), 4-dimethylaminopyridine (122 mg.) and methanesulphonamide (95 mg.)in dry dichloromethane (20 ml.) was treated with a solution ofdicyclohexylcarbodiimide (206 mg.) in dichloromethane (2 ml.). Themixture was stirred overnight, filtered, and the filtrate wasevaporated. The residual oil was partitioned between saturated aqueoussodium carbonate solution (50 ml.) and ether (50 ml.), and the aqueousphase was washed with more ether (2×25 ml.). The aqueous phase wasacidified with hydrochloric acid (2M) and extracted with ethyl acetate(3×25 ml.). The combined extracts were washed with saturated brine,dried (MgSO₄) and evaporated to give an oil which on columnchromatography, eluting with toluene/ethyl acetate/acetic acid (80:20:2v/v) gaveN-methanesulphonyl-5(Z)-7-(2,2-dimethyl-4-phenyl-1,3-dioxan-cis-5-yl)heptenamide,as a colourless oil (100 mg.); NMR: 1,2-2.5 (9H,m), 1.55 (6H,s), 3.25(3H,s), 3.7-4.3 (2H,m), 5.1-5.5 (3H,m), 7.1-7.4 (5H,br.s), 8.4 (1H,brs).

EXAMPLE 11

The following additional deprotection procedure illustrates theproduction of compounds of the formula I wherein one of Ra, Rb andbenzene ring B bears an aromatic hydroxy group:

A portion (2.1 ml.) of a 0.5M solution of sodium thioethoxide inN,N-dimethylformamide was added under nitrogen to5(Z)-7-(2,2-dimethyl-4-o-methoxyphenyl-1,3-dioxan-cis-5-yl)heptenoicacid (104 mg.). The mixture was heated under reflux for 1.1 hours andthen diluted with ice-water to a total volume of 25 ml. The aqueousmixture was acidified to pH 4 with acetic acid and extracted with ethylacetate (2×15 ml.). The extracts were washed with saturated brine, dried(MgSO₄) and evaporated. The oil obtained was purified by columnchromatography on silica (12 g.) eluting with 80:20:2 (by volume)toluene/ethyl acetate/acetic acid to give5(Z)-7-(2,2-dimethyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl)heptenoicacid as an oil (25 mg.);

NMR (400MHz): 1.50 (6H,s), 2.22 (9H,m), 3.97 (2H,m), 5.31 (3H,m), 6.98(4H,m), 8.38 (2H,s).

EXAMPLE 12

This Example demonstrates isomerisation of a cis- to a trans- paraconicacid of formula V.

A mixture of [2,3-cis]- and[2,3-trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid(1.0 g.) and p-toluenesulphonic acid monohydrate (0.15 g.) in toluene(20 ml.) was heated under reflux for 2 hours. The hot solution was thenallowed to cool to give a white crystalline precipitate enriched in[2,3-trans]- tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid,as judged by NMR spectroscopy.

EXAMPLE 13

This Example illustrates the production of an optically active form of acompound of formula I:

(i) A solution of d-ephedrine (61.2 g.) in hot ethyl acetate (150 ml.)was added to a solution of[2,3-trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3-furancarboxylic acid(87.6 g.) in hot ethyl acetate (350 ml.). The mixture was allowed tocool to room temperature during 2 hours and the crystalline salt whichhad formed was separated by filtration to give 62 g. of solid materialhaving ²⁵ [α]_(D) +40.2° (methanol). This material was recrystallisedtwice from ethyl acetate to give 48 g. of optically pure solid ²⁵[α]_(D) +50.3° (methanol). This solid was added to ethyl acetate (1liter) and 2M hydrochloric acid (150 ml.). The ethyl acetate layer waswashed with brine (2×100 ml.) until the pH of the washings was pH2-3,and then dried (MgSO₄) and evaporated. The residue was dissolved inboiling toluene (200 ml.). Insoluble material was removed by hotfiltration. The filtrate was allowed to cool to give (+)- [2,3trans]-tetrahydro-2-o-methoxyphenyl-5-oxo-3- furancarboxylic acid (A)(27.4 g.) ²⁵ [α]_(D) +33.0° (methanol). Recrystallisation from toluenegave material of ²⁵ [α]_(D) +33.8° (methanol), m.p. 125°-127° C.(decomposition), shown to be >98% optically pure by conversion of asmall sample to its (-)-amyl ester and examination of the ¹³ C NMRspectrum.

(ii) A solution of A (97.5 g.) in dry tetrahydrofuran (150 ml.) wascooled to 15° C. and treated with a solution of borane intetrahydrofuran (500 ml. of a 1M solution) with the temperaturemaintained at 20°-25° C. After 30 minutes the reaction was complete (asjudged by TLC analysis) and water (200 ml.) was added slowly todecompose the excess borane. The mixture was concentrated in vacuo andthe residue was mixed with ethyl acetate (500 ml.). The organic layerwas washed successively with saturated potassium carbonate solution(2×100 ml.) and saturated brine, dried (MgSO₄), and evaporated to give[4,5-trans]-tetrahydro-4-hydroxymethyl-5-o-methoxyphenylfuran-2-one (B)as a viscous oil (81.8 g.), having ²⁵ [α]_(D) -14.2° (methanol) and asatisfactory NMR spectrum (d₆ -acetone): 2.6 (3H,m), 3.7 (2H,m), 3.8(3H,s), 4.1 (1H,br), 5.55 (1 H,m), 6.8-7.5 (4H,m).

(iii) A solution of B (obtained above) in 1,2-dimethoxyethane (150 ml.)and dry toluene (500 ml.) was cooled under a nitrogen atmosphere to -60°C. A toluene solution of diisobutylaluminium hydride (672 ml. of 1.23Msolution) was then added slowly. After 30 minutes the reaction wasquenched by addition of methanol (50 ml.) and the mixture allowed towarm up to room temperature. 2M Hydrochloric acid (1 liter) and ethylacetate (500 ml.) were then added and the mixture stirred. The aqueousphase was separated and extracted with ethyl acetate (2×500 ml.). Theethyl acetate phase and extracts were combined, dried (MgSO₄) andevaporated. The residual oil was dissolved in hot toluene (500 ml.). Thesolution obtained gave on cooling(-)-[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-o-methoxyfuran(C) as a white solid (63.3 g.), ²⁵ [α]_(D) -24.2° (methanol, m.p.110°-111° C., having a satisfactory NMR spectrum: 1.5-2.4 (3H,m),3.4-4.0 (2H,m), 3.8 (3H,s) 4.2-4.8 (2H,br), 5.25 (1H,m), 5.6 (1H,m),6.8-7.9 (4H,m).

(iv) A solution of C (63.3 g.) in dry tetrahydrofuran (200 ml.) wasadded at ambient temperature to a red ylid solution [obtained by heating4-carboxybutyl)phosphonium bromide (505 g.) and potassium t-butoxide(255.5 g.) in dry toluene (2 liters) at 90° C. under a nitrogenatmosphere]. The red mixture obtained [which contained the dipotassiumsalt of(-)-erythro-4-hydroxy-3-hydroxymethyl-4-o-methoxyphenylbutyraldehyde insitu] was stirred for 20 minutes after which time TLC analysis indicatedcomplete reaction. Water (1 liter) was then added. The phases wereseparated and the aqueous phase extracted with ethyl acetate (3×500ml.). The extracts were discarded. The aqueous phase was then acidified(pH 4) by addition of oxalic acid and then extracted with ethyl acetate.The combined extracts were washed with saturated brine, dried (MgSO₄)and evaporated. The residue was triturated with ethyl acetate (100 ml.)and solid material removed by filtration. The filtrate was evaporated togive(-)-erythro-5(Z)-9-hydroxy-8-hydroxymethyl-9-o-methoxyphenyl-5-nonenoicacid (D) as a viscous oil (65.9 g.) ²⁵ [α]_(D) -61° (methanol), havingan NMR spectrum essentially the same as that in Example 5.

(v) A mixture of D(2.0 g.) and p-toluenesulphonic acid (50 mg.) in2,2-dimethoxypropane (10 ml.) was stirred for 1 hour. Triethylamine (1ml.) and ether (10 ml.) were then added and the mixture evaporated. Theresidue was extracted with ether (30 ml.). The

ethereal solution was washed with water (2×10 ml.), dried (MgSO₄) andevaporated. The residual oil was purified by chromatography on silica(30 g.) using 25% v/v ethyl acetate in toluene as eluant to give(-)-5-(Z)-7-(2,2-dimethyl-4-o-methoxyphenyl-1,3-dioxan-cis-5-yl)heptenoicacid as a viscous oil (1.5 g.), ²⁵ [α]_(D) -127.6° (ethyl acetate),having an NMR spectrum essentially identical with that given in Example7. ##STR1##

What is claimed is:
 1. A process for the manufacture of a(4-phenyl-1,3-dioxan-cis-5-yl)alkenoic acid of the formula I set outherein wherein Ra and Rb are independently hydrogen, (2-6C)alkenyl,(1-8C)alkyl optionally bearing up to three halogeno substituents,pentafluorophenyl, aryl or aryl-(1-4C)alkyl, the latter two of which mayoptionally bear up to three substituents selected from halogeno,(1-6C)alkyl, 1-6C)alkoxy, (1-4C)alkylenedioxy, trifluoromethyl, cyano,nitro, hydroxy, (2-6C)alkanoyloxy, (1-6C)alkylthio,(1-6C)alkanesulphonyl, (1-6C)alkanoylamino, and oxapolymethylene of 2 to4 carbon atoms, provided that when both Ra and Rb are alkyl or alkenyl,the total number of carbon atoms in Ra and Rb taken together is 8 orless; or Ra and Rb together form polymethylene of 2 to 7 carbon atoms,optionally bearing one or two (1-4C)alkyl substituents; Rc is hydroxy,(1-6C)alkoxy or (1-6C)alkanesulphonamido; n is 1; A is ethylene orvinylene; Y is polymethylene of 2 to 5 carbon atoms optionally bearing(1-4C)alkyl as a substituent; benzene ring B optionally bears one or twosubstituents selected from halogeno, (1-6C)alkyl, (1-6C)alkoxy, hydroxy,(1-6C)alkanoyloxy, (1-6C)alkanoylamino, trifluoromethyl and nitro; andthe substituents at positions 4 and 5 of the dioxane ring havecis-relative stereochemistry; or for those compounds wherein Rc ishydroxy, a salt thereof with a base affording a physiologicallyacceptable cation; which is characterised by carrying out the steps of:(i) reacting an erythro-4-hydroxy-3-hydroxymethyl-4-phenylbutyraldehydeof the formula II, or an alkali metal salt thereof, or the corresponding[2,3-trans]-tetrahydro-5-hydroxy-3-hydroxymethyl-2-phenylfuran of theformula IIa, wherein benzene ring B has the meaning defined above, andthe hydroxy and hydroxymethyl groups in formula II have the indicatedcis-relative stereochemistry, with an ylid of the formula (Rd)₃ P═CH.YCO.Q wherein Rd is (1-6C)alkyl or aryl and Q stands for --OM or --NM.SO₂Re in which M is an alkali metal, Re is (1-6C)alkyl and Y has themeaning defined above, to give after acidification an erythrodiol of theformula III wherein benzene ring B has the meaning defined above, and Rfis hydroxy or (1-6)C alkanesulphonamido; and(ii) reacting the diol offormula III, or a mono (1-6C)alkanesulphonyl or arenesulphonyl esterthereof, with a carbonyl compound of the formula RaRb.CO, or an acetal,hemiacetal or hydrate thereof; whereafter: when a compound of formula Iwherein A is ethylene is required, the corresponding compound of formulaI wherein A is vinylene is hydrogenated in the presence of a suitablecatalyst;when a compound of formula I wherein Ra or Rb is hydroxyphenyl,or benzene ring B bears a hydroxy substituent is required, thecorresponding compound of formula I wherein the hydroxy group isprotected by a trimethylsilyl, (1-6C)alkyl, acyl or benzyl protectinggroup is deprotected; when an optically active form is required, steps(i) and (ii) above are carried out starting with an optically activealdehyde of formula II or furan of the formula IIa, or a racemic form ofa compound of formula I wherein Rc is hydroxy is resolved by reactionwith an optically active form of a suitable organic base, by aconventional procedure; when a pharmaceutically acceptable salt isrequired, a compound of formula I wherein Rc is hydroxy is reacted withthe appropriate base affording a physiologically acceptable cation; orwhen a (1-6C)alkyl ester or (1-6C)alkanesulphonamide is required, thecorresponding compound of formula I wherein Rc in hydroxy in racemic oroptically active form, or a reactive derivative thereof, is reacted withthe appropriate (1-6C)alkanol or (1-6C)alkanesulphonamide, or with analkali metal salt thereof.
 2. A process according to claim 1characterised in that in the starting materials:(i) Ra and Rb are bothhydrogen, methyl, ethyl, propyl, butyl or trifluoromethyl; (ii) Ra andRb together form trimethylene, tetramethylene, pentamethylene,hexamethylene or a group of the formula: --CH₂ CH₂.CHCH₃.CH₂ CH₂ --; or(iii) Ra is (3-8C)alkyl, trifluoromethyl, chloromethyl, 2-chloroethyl,pentafluorophenyl, phenyl, benzyl or naphthyl, the last three of whichmay optionally bear 1 or 2 halogeno, (1-4C)alkyl, (1-4C)alkoxy,trifluoromethyl, hydroxy, cyano, (1-4C)alkylthio or (1-4C)alkanoylaminosubstituents, or a methylenedioxy or methyleneoxymethylene substituent,and Rb is hydrogen;benzene ring B is unsubstituted or is 2-halogeno-,2-(1-4C)alkyl-, 2-(1-4C)alkoxy-, 2-hydroxy- or 3-halogeno-phenyl; Ra andthe substituents at the 4- and 5-positions of the dioxane ring havecis-relative stereochemistry; n is 1; and Y is trimethylene.
 3. Aprocess according to claim 1 characterized in that in the startingmaterials Ra is methyl, ethyl, isopropyl, 2-chlorophenyl,2-methylphenyl, 2-ethylphenyl; 3-fluorophenyl, 3-chlorophenyl,3-methylthiophenyl, 4-fluorophenyl, 4-chlorophenyl, 4-methoxyphenyl,3,4-methylenedioxyphenyl or 3,4,(methyleneoxymethylene)phenyl, and Rb ishydrogen; or Ra and Rb are both methyl or ethyl, or together formpentamethylene, hexamethylene or (3-methyl)pentamethylene; benzene ringB is unsubstituted or bears an o-methoxy, o-hydroxy, o-fluoro, o-methylor o-chloro substituent; Ra and the substituents at the 4- and5-positions of the dioxane ring have cis-relative stereochemistry; n is1; and A is trimethylene.